the only question that I can provide a complete answer for here is the one about the VPT round with the four red “dots” that form an “X” on the headstamp. That is a proof load, and that marking has been used on other calibers. I have a loaded round and a fired case from Mauser, Oberndorf. I visited the factory in 1972 and at that time, they were producing their post-war series of Luger-type pistols, primarily when I visited in caliber 7.65mm Parabellum. They were using Finnish proof loads with the marking described in their proof room. I picked up one of the fired cases, and asked if I could keep it as a souvenir. I hinted for a loaded round.
Arsenal Number 141 is used by China. I suspect it is the same factory as “11” but I don’t know that, and I don’t know nayone who knows which factories these actually are. If anyone knows the actual factory name or location for Arsenal 17 or 81, I would love to know it!
I don’t know enough to answer your question about whether Arsenal 81 made brass-washed steel cases in 1964, but I have in my dupes a round from arsenal 31 dated 66 that has a brass-washed case, so certainly BWS cases were not unknown to the Chinese in the 1960s.
For Arsenal 21 in Poland, the last full name I have for this factory is Zaklady Metalowe, Marka Export Solidnosc Knokurencyjnosc Otwartosc, Skarzysko-Kamienna. These factory names in former communist-controlled countries are changing right and left, so that may not be current.
Most of the Syrian 7.62 x 39 that has gone through my hands (we had, years ago, two hundred boxes of it in a mixed shipment of this claiber from Isreal that contained 7.62 x 39 ammo from all over the communist world),
had a very narrow case mouth seal that on first glance appears black, but under a magnifying glass in good light is dark purple. I would say that is the norm, and it certainly is ordninary ball ammunition. I still have a couple of rounds of it in my dupes afte 20 or so years. The primer seal is the same color, but since there is more of it than the thin line at the neck, it is more obviously purpole. I have never had a Syrian round with no case mouth seal, but then, I have only had a couple of dates so that mean nothing, I realize. If yours is, upon close examination, truly black, I have no idea what it signifies.